This invention relates to the preparation of dental impressions of prepared teeth for fitting jacket crowns, bridgework and the like, and, more particularly, to a method and apparatus for preparing dental impressions without retraction of the gingival tissue.
In the preparation of teeth for fitting of full or partial jacket crowns, circumferential reduction of the tooth is required to compensate for the wall thickness of the crown. This reduction may be accomplished freehand, but is preferably conducted with a dental instrument such as described in U.S. Pat. Nos. 3,445,935 and 3,600,810. The use of such an instrument assures uniform reduction of the tooth below the gingival margin with slightly tapered walls. The length of the tooth is reduced freehand as required to accept the crown.
Following reduction of the tooth, it is necessary to take a dental impression of the prepared tooth and the associated teeth in that jaw in order for the dental technician to fabricate the desired crown or bridgework. In forming the dental impression, it is essential that the detail of the gingival crevice and shoulder of the prepared tooth be precisely obtained in order to assure proper fit of the crown for good functional and cosmetic effect.
It has been the general practice in the dental profession to retract the gingival tissue to provide access for the impression material into the gingival crevice. Retraction may involve the physical removal of tissue by surgical or electrosurgical means, or may be accomplished by means of retraction strings which are chemically treated and packed into the gingival crevice. Such retraction is necessarily limited to healthy tissue, and the retraction method must be carefully performed to avoid tissue damage and permanent recession of the gingiva.
Retraction is often associated with problems relating to laceration of the tissue and hemorrhage, debris left in the prepared area, irreversible tissue damage caused by prolonged contact with the chemical agent in the retraction string or by extending surgical alteration too far into the gingival crevice, and adverse physiological reactions of some patients to the chemicals of the retraction strings, particularly those associated with high blood pressure or heart disease.
It has been suggested in my earlier patent, U.S. Pat. No. 4,074,436, that the need for retraction may be eliminated by fixing an open copper tube in the impression tray at a position to enclose the prepared tooth, with the end of the tube extending into the gingival crevice and contoured to conform to the contour of the gingival margin. The tray is loaded with impression material around the open tubes and positioned firmly within the mouth of the patient. Additional impression material is then injected from a syringe into the copper tubes with sufficient pressure to force the material into the gingival crevice. After allowing the impression material to harden, the tray is carefully removed along the axis of the prepared tooth while taking precautions against bending the copper tube. While the aforedescribed copper tube method is effective to obtain detailed impressions without retraction of the gingival tissue, it has certain other disadvantages. In particular, it requires the services of a dental technician or laboratory to contour the tip of copper tube to the shape of the gingival margin and to secure the copper tube in an acrylic impression tray as described in U.S. Pat. No. 4,074,436. There is also some risk of damage to the gingival tissue during the impression procedure if the end copper tube is inserted too deeply into the gingival crevice. Moreover, the copper tube cannot be contoured as described in U.S. Pat. No. 4,074,036 until after the basic dental instrument used in the tooth reduction is prepared as described in my patent, U.S. Pat. No. 3,600,810. These and other disadvantages of the copper tube method are resolved by means of the present invention.
It is accordingly an object of the present invention to provide a method for forming impressions of a prepared tooth without retraction of the gingival tissue. It is another object of this invention to provide a method and apparatus for assuring the formation of good impressions without risk of damage to the gingival tissue. It is a further object of this invention to provide apparatus for forming impressions which can be used by the dentist without the expense or delay involved in utilizing the services of a dental laboratory. These and other objects of the present invention will be apparent from the ensuing description and claims.